This patch adds 3 new variables and sysctls to tune them (by one "next_id"
variable for messages, semaphores and shared memory respectively).
This variable can be used to set desired id for next allocated IPC object.
By default it's equal to -1 and old behaviour is preserved.
If this variable is non-negative, then desired idr will be extracted from it
and used as a start value to search for free IDR slot.

Notes:
1) this patch doesn't garantee, that new object will have desired id. So it's
up to user space how to handle new object with wrong id.
2) After sucessfull id allocation attempt, "next_id" will be set back to -1
(if it was non-negative).

ipc_kern_table[] is (badly) documented in
Documentation/sysctl/kernel.txt. Can we at least mention these
controls in there? Better, create a new way of properly documenting
each control and document these three in that manner? Better still,
document all the other ones as well ;)

The patch adds these controls to CONFIG_CHECKPOINT_RESTORE=n kernels.
Why is this?